0:02

Hello and welcome to Noon Conferences hosted by MRI Online.

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In response to changes happening around the world

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right now and the shutting down of in-person

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events, we've decided to provide free daily

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noon conferences to all radiologists worldwide.

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Today we're joined by Dr. Nichola

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Schieda for a lecture on renal imaging.

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Dr. Schieda is a genitourinary radiologist, sorry, radiologist

0:23

and director of abdominal MRI at the Ottawa Hospital

0:27

and Associate Professor at the University of Ottawa.

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Active in clinical research, Dr. Schieda's

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interests relate to imaging diagnosis of

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adrenal, renal, and prostate malignancies.

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A reminder, there will be a Q&A session

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at the end of the lecture, so please use

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the Q&A feature to ask your questions.

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We'll get to as many as we can before time is up.

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That being said, thank you all so much for joining us

0:46

today. Dr. Schieda, I'll let you take things from here.

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Great.

0:49

Thank you for the introduction and, uh, for the invitation

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to lecture, um, as part of your educational platform.

0:57

My name's Nick Shida.

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I'm an associate professor at the University of Ottawa.

1:01

In the next 35 to 40 minutes, we'll be reviewing

1:05

CT and MR of, uh, cystic renal masses with heavy

1:08

emphasis on the recently released Bosniak version

1:13

2019 classification of renal cystic masses.

1:17

I have no relevant financial disclosures.

1:20

I am, however, one of the authors of

1:22

the Bosniak version 2019 proposal.

1:26

The outline for the lecture.

1:27

We'll start with a background of imaging and

1:30

clinical management of cystic renal masses.

1:33

Then we'll discuss limitations of the original

1:35

Bosniak classification and rationale for change,

1:39

and then the bulk of the lecture will be spent

1:41

on a pictorial review of proposed changes to CT

1:45

and MRI classification of renal cystic masses.

1:49

A very brief summary of the emerging evidence on

1:52

Bosniak version 2019 will be presented at the end

1:55

of the lecture before I field a couple of questions.

1:59

So, as most of you are aware, the original Bosniak

2:02

classification was devised by Dr. Bosniak in the 1980s

2:07

and is a Likert-type probability scale to indicate

2:10

the likelihood of malignancy in cystic renal mass.

2:14

The original classification consisted of four categories.

2:19

With definitely benign on one end of the spectrum and

2:21

definitely malignant on the other end of the spectrum.

2:25

And the last revision proposed by Dr. Bosniak

2:28

was the addition of a category II F, so a fifth

2:32

Likert category to include cystic masses that

2:35

were likely benign, but that required follow-up.

2:39

The probability of malignancy among the Bosniak

2:42

categories from the original classification

2:45

has been evaluated in two large meta-analyses.

2:49

These show, um, difficult to characterize definitively

2:54

benign lesions since these cystic masses or cysts only

2:58

rarely undergo pathologic evaluation, approximately 0%

3:03

rate of malignancy in category II, probably benign masses.

3:09

Less than 1% rate of malignancy in II F masses.

3:14

However, among the 10% of masses that progress, 85% are

3:19

eventually malignant after surgery or biopsy confirmation.

3:24

A 50/50 chance of malignancy in the category

3:27

three and greater than or equal to

3:30

90% chance of malignancy in the category four.

3:35

Recently, management of cystic RCC has undergone some

3:40

thoughtful consideration by our urological colleagues.

3:43

Uh, this relates to pathological awareness that these

3:47

tumors are usually low grade, uh, typically grade one

3:50

or two out of four, um, clear cell or papillary RCC.

3:55

They have an extremely low or negligible

3:57

risk of local recurrence after surgery.

3:59

They very rarely progress locally

4:02

and even rarely metastasize.

4:05

And when compared to solid, solid RCC of

4:07

similar stage and size, they have been

4:10

shown to have better long-term survival.

4:14

So the management of cystic renal masses is changing.

4:17

As we know, most Bosniak II F are managed

4:20

conservatively with active surveillance.

4:22

However, in modern clinical practice, many Bosniak three.

4:26

An increasing number of even Bosniak four

4:28

cystic renal masses may be managed with

4:31

active surveillance in selected patients.

4:34

Adoption of active surveillance in cystic renal masses

4:37

is effective because most Bosniak II F and half

4:41

of Bosniak three cystic masses are actually benign.

4:45

And as we recently saw in the previous slide,

4:47

even when malignant, these tumors tend to have a

4:50

very good prognosis. Limitations of the current.

4:55

The original Bosniak classification are

4:57

therefore that many benign masses are resected,

5:01

particularly those included in category three.

5:04

Inter-reader variability is at best moderate. Malignancy

5:08

rates within the original categories are shown to

5:13

have been widely variable, and the original Bosniak

5:16

classification does not formally incorporate MRI and

5:19

ultrasound or account for all cystic renal masses.

5:23

So these limitations led to a proposal in

5:26

2019 to update the Bosniak classification.

5:31

Uh, specifically aims of Bosniak version 2019 were

5:34

to include a larger proportion of masses into lower

5:38

Bosniak classes, thereby emphasizing specificity

5:41

for diagnosis of renal cell carcinoma with ideally

5:45

maintained sensitivity, defining imaging features,

5:49

terms, and classes fully to reduce variability.

5:54

To enhance accuracy, in particular, emphasize

5:57

specificity to formally incorporate MRI and, to some

6:01

extent, ultrasound, and to attempt to include more

6:05

completely characterized renal masses that were not

6:07

initially characterized in the original classification.

6:12

So these are some images from the original,

6:14

uh, paper that was published in Radiology.

6:17

And, um, I, I won't spend too much time

6:19

on this slide, but suffice it to say that,

6:22

basically every term or feature in a cystic renal mass

6:26

has been attempted to be defined rigorously, including

6:30

what is a septum, how thick a septum is or should be,

6:34

or can be, uh, wall thickness and differences in

6:38

protrusions that may arise on walls or septa, uh, with

6:42

terms such as irregularity and nodules fully defined.

6:47

Here's a table depiction of the

6:49

updated, uh, Bosniak version 2019.

6:53

Uh, so you can see that there's, um, still five classes, uh,

6:57

I, II, II F, III, and IV, and includes both CT and MRI.

7:04

So one question, which commonly, um, arises in

7:07

clinical practice, especially amongst trainees, is when

7:10

do you apply the Bosniak criteria and when don't you?

7:13

And it turns out this was actually never really defined.

7:16

The definition of what constitutes a cystic

7:19

mass actually varies in, uh, the literature.

7:22

The Bosniak version 2019 criteria defines a

7:25

cystic mass as one in which less than 25%

7:28

of the mass is composed of enhancing tissue.

7:31

So if there's more than 25% enhancing tissue,

7:35

it's not considered a cystic renal mass.

7:37

It's considered a solid renal mass, and therefore

7:39

the Bosniak version 2019 criteria is not applicable.

7:44

There are additional caveats to when to apply the

7:47

Bosniak version 2019 criteria, including in patients

7:51

who have a genetic syndrome that predisposes to

7:54

renal cell carcinoma, such as Von Hippel-Lindau.

7:58

So what we'll do next is look at the different

8:02

types, um, of classes within the Bosniak version

8:05

2019 for CT and each type within each class.

8:11

So the first class is the most basic.

8:14

Uh, these are simple cysts.

8:15

So this is the only class where

8:17

the term simple cyst can be used.

8:20

And these include well-defined, um, having a thin, so less

8:24

than two millimeters, smooth wall, and are consisting of

8:27

homogeneous simple fluid with no septa or calcifications.

8:32

And one new addition in class one is

8:35

the concept that the wall may enhance.

8:38

As long as it's still thin and smooth.

8:42

Uh, one of the big differences between version 2019

8:46

and the original classification is in class two.

8:49

So you'll see from the table, um, and your

8:52

own review of the classification that there's

8:54

an expanded number of class two masses.

8:58

And this is because we attempted to enable

9:01

classification of all cystic masses.

9:04

Uh, so a lot of cystic masses were previously

9:07

not characterized or undefined in the original

9:10

classification, necessitating the use of a

9:13

dedicated renal mass CT or MRI protocol.

9:16

However, evidence in the recent literature shows

9:19

that many of these uncharacterized masses in

9:22

the original classification have a very high

9:25

likelihood of being benign or non-aggressive,

9:28

and do not necessarily require the increased cost

9:32

and morbidity of a renal mass protocol CT or MRI.

9:37

So the first type in class two is very

9:40

similar to the original classification,

9:42

and this include it, it is septated cysts.

9:46

Uh, so a septated cyst in class two should

9:48

have a thin wall and a thin and few, one

9:52

to three septa, and the wall may enhance.

9:56

So one of the definitions is that a septum is a

9:59

linear or curvilinear structure that connects

10:01

two surfaces, and in Bosniak version 2019.

10:05

Thin is defined as less than or equal to two

10:08

millimeters, and few is defined as one to three.

10:13

The next type within class two for CT is a

10:16

greater than or equal to homogeneous hyperdense

10:20

mass measuring 70 Hounsfield units or greater.

10:24

So here's an example of a homogeneously hyperdense

10:28

lesion that measures 78 Hounsfield units.

10:31

This has been shown in several studies to have a

10:35

very high likelihood of being benign in this patient.

10:38

A follow-up confirmation ultrasound

10:39

confirmed a hemorrhagic cyst.

10:43

Um, previously in the original Bosniak classification,

10:47

hyperattenuating masses that were greater

10:49

than three centimeters were indeterminate, uh,

10:53

or classified as II F in the version 2019.

10:58

Greater than three centimeter

10:59

homogeneously hyperattenuating masses.

11:02

We do recommend MRI because these lesions are very rare.

11:06

Um, typically when they're above three

11:08

centimeters, they tend to be heterogeneous

11:10

and usually would necessitate an MRI.

11:14

But if for some rare instance you might encounter

11:18

a homogeneous renal mass that's greater than

11:21

70 HU, uh, on unenhanced CT and homogeneous.

11:26

Even though it most likely represents a hemorrhagic

11:28

cyst, the cautious approach in version 2019

11:31

was to recommend an MRI for those lesions.

11:35

The third type in class two for CT is a nonenhancing

11:39

greater than 20 HU mass, a dedicated renal mass protocol CT.

11:44

So this is an example of a soft tissue attenuation

11:48

lesion in the interpolar region of the right kidney

11:51

that measures 36 Hounsfield units at unenhanced CT.

11:55

Nephrographic phase CT does not change by greater than

11:58

10 HU or 20 HU to be definitively enhancing, uh, which

12:03

was confirmed to be a minimally complex or proteinaceous

12:09

cyst at MRI, where there's no enhancement at subtraction.

12:14

One important pitfall with that type is

12:17

that confirm the absence of enhancement.

12:20

That must be at a renal mass protocol CT.

12:24

We do know that a substantial proportion of papillary RCCs

12:29

will not enhance by 20 Hounsfield units or greater at

12:32

corticomedullary and even nephrographic phase enhanced CT.

12:36

However, the majority at nephrographic phase enhanced

12:40

CT will at least be in the indeterminate range.

12:42

So here's an example of a small papillary tumor

12:45

in the interpolar region of the left kidney,

12:47

which does not enhance. Comparing the unenhanced and the

12:51

corticomedullary phase, there's a difference of only 10 HU.

12:54

It is in the indeterminate range of enhancement at nephro-

12:58

graphic phase and was confirmed to be enhancing at MRI

13:02

and subsequently proven to be a papillary tumor at biopsy.

13:08

The fourth type of class two in CT is a

13:11

simple cyst-appearing mass at unenhanced CT.

13:15

So this is something that we apply

13:17

readily in clinical practice.

13:19

It's validated in the literature, but was

13:21

not included in the original classification.

13:24

This technically would be an

13:26

indeterminate renal cyst or cystic mass.

13:29

Um, so here we see a homogeneous cyst that

13:32

measures two Hounsfield units, and a subsequent

13:35

follow-up corticomedullary and nephrographic phase.

13:39

Here we see the nephrographic phase.

13:40

There's no enhancement in the cyst, so.

13:43

You can confidently call a simple cyst-appearing

13:46

mass at unenhanced CT when it's homogeneous and

13:49

measures less than or equal to 20 Hounsfield units.

13:53

This is another pitfall of the class two variants in CT.

13:59

Here we see a necrotic mass, which has a central

14:03

low attenuating area that is fluid density.

14:07

And as you can see on the nephrographic

14:09

phase enhanced CT, there is enhancement of the

14:12

periphery of the mass where the viable tumor is.

14:15

So one of the really important features when applying

14:19

this subtype of class two is that the mass be

14:22

completely homogeneous in addition to fluid attenuation.

14:27

So the pitfall is placing a region of interest within

14:30

the center of the mass and getting water attenuation and

14:33

calling it a cyst, when in fact it's a necrotic tumor.

14:38

Moving on to another subtype within class two.

14:42

These are 21 to 30 Hounsfield unit homogeneous

14:46

masses at portal venous phase enhanced CT.

14:49

So this is another commonly encountered lesion in clinic.

14:59

It's above fluid attenuation, usually because the lesion

15:04

is endophytic and there is pseudoenhancement, which

15:08

is spuriously raising the attenuation of the cyst.

15:11

In this case, a T2-weighted MRI and post-

15:14

contrast subtraction image confirmed a simple cyst.

15:17

Now this is important.

15:19

It's important to recognize that this does not mean that

15:22

there are no RCCs, particularly papillary RCC, which

15:26

are less than 40 Hounsfield units at enhanced CT.

15:30

However, when evaluating these lesions over a population,

15:34

the likelihood is so low that, uh, that the evidence

15:39

suggests that these should be included in Bosniak class two.

15:45

Um, I believe this is the last class two variant,

15:48

and it's also a new entry into class two to

15:52

acknowledge a commonly encountered lesion in clinical

15:55

practice, which is a homogeneous too-small-to-

15:58

characterize hypodensity in the renal cortex.

16:02

Um, as you can see in this case, which turned out

16:04

to be a simple cyst on follow-up MRI, abundant

16:08

classification is something that's, uh, within class two.

16:13

Um, so for renal masses that have abundant

16:16

thick or nodular calcification, MRI is

16:18

recommended to evaluate for enhancing elements.

16:21

Prior to assigning a Bosniak class, it's difficult

16:24

to assign a Bosniak class at CT in a mass that

16:27

has extensive calcification because we're not

16:30

able to see the internal components of the mass.

16:34

So, for example, in this case, there's a lesion

16:36

arising from the upper pole of the left kidney.

16:38

It has heavy calcification, which limits

16:41

assessment of the internal architecture.

16:44

A subsequent MRI was performed,

16:46

showing that it was a simple cyst.

16:48

Um, the MRI is advantageous in this situation because

16:51

the calcifications are not readily detectable.

16:55

Here's another example of a densely calcified

16:57

lesion, partly within the renal sinus.

17:01

As you can see on CT, it's very

17:03

difficult to assess this lesion.

17:05

Its internal structure.

17:07

Subsequent MRI was performed, and you can see

17:09

on this, uh, post-contrast image that there's a

17:12

thickened septum, which is slightly irregular.

17:15

And, uh, so at CT indeterminate,

17:18

at follow-up MRI, class three.

17:22

So moving on to class II F. This constitutes the same.

17:27

Pr, same group of lesions that were included in the

17:31

original classification, but with more rigorous definition.

17:34

So the, these cystic masses are those that

17:37

have smi, smooth, minimal thickening of the

17:39

wall, or smooth, minimal thickening of one or

17:42

more septa, or many smooth, thin enhancing septa.

17:48

So definitions: thin, less than or equal to two

17:51

millimeters; minimally thickened, three millimeters;

17:54

thick, greater than or equal to four millimeters.

17:57

And in terms of number of septa, one to three is

18:00

few, and greater than or equal to four is many.

18:04

Another point of importance is many cystic masses often

18:08

show multiple features, so they may have thick septa,

18:11

minimally thickened septa, increased number of septa.

18:15

You have to apply the highest feature to assign the Bosniak

18:19

class, and the combination of numerous features do not add

18:23

up or, um, upgrade, um, a cystic mass into another category.

18:28

So if you have a cystic mass that has many

18:33

minimally thickened septa, this would still

18:36

be a category or class II F. The combination

18:39

of the two features does not make it a three.

18:43

Moving on to class three.

18:46

Uh, these are cystic masses which show one or more enhancing

18:49

thick, so greater than or equal to four millimeters, or

18:53

enhancing irregular, displaying less than or equal to three

18:56

millimeter obtusely margin protrusions, walls, or septa.

19:00

So this is an example on the left of a patient

19:03

with autosomal dominant polycystic kidney disease.

19:06

There is a cystic mass in the

19:08

posterior aspect of the right kidney,

19:10

which has a thick, smooth wall.

19:12

It's four millimeters.

19:13

It was removed and confirmed to

19:15

be a cystic renal cell carcinoma.

19:18

On the other side, there's a different

19:21

patient with a lesion that's endophytic.

19:24

So this patient has this lesion, has multiple septa, and one

19:28

of those septa has a protrusion, which has obtuse margins

19:32

to the underlying septum, and it measures three millimeters.

19:36

So you can see that that protrusion has

19:38

obtuse margins to the underlying septum.

19:42

So this is termed an irregularity, not

19:44

a nodule, which we'll go over later.

19:47

So this makes it a class three.

19:50

So moving on to class four, and the

19:52

distinction between class four and class

19:54

three and lower is the presence of a nodule.

19:57

So when there's a nodule, it's a class four.

20:00

These are masses which show enhancing nodules.

20:04

Nodules are defined as protrusions that have

20:06

obtuse margins to the underlying wall or septum,

20:10

measuring four millimeters or larger, or that have

20:13

acute margins to the underlying wall or septum.

20:17

So these are two examples of nodules that have obtuse

20:20

margins, uh, just like the preceding case to the

20:23

underlying wall or septum, but they both measure

20:26

more than four millimeters in size, making them

20:30

class four due to the presence of a nodule.

20:36

So an important definition is the presence of a

20:38

nodule, because that's the highest feature that a

20:41

cystic mass can have, and it's a protrusion arising

20:45

from the wall or septum that can be any size if it

20:49

has acute margins to the underlying wall or septum,

20:52

or greater than or equal to four millimeters if it

20:54

has obtuse margins to the underlying wall or septum.

20:58

Nodule is a feature of Bosniak four.

21:02

Here's another example of a nodule.

21:04

So I'm showing lots of nodules because this is

21:06

the most important and the highest feature

21:09

in the Bosniak version 2019 classification.

21:12

This is a three-millimeter protrusion; however, it

21:16

has acute margins to the underlying wall.

21:19

So the difference between this nodule and the others is that

21:23

the margins to the underlying wall or septum are acute,

21:26

as opposed to obtuse.

21:27

So even though it's less than four

21:29

millimeters, it constitutes the definition

21:32

of a nodule and is a category four.

21:36

Okay, so moving on to MRI.

21:37

So there's a lot of overlap and some differences

21:41

comparing the MRI column and the CT column.

21:44

So there'll be some repetition.

21:46

This is the same patient for class one that I showed for CT.

21:50

So it's a well-defined, thin, less than

21:52

or equal to two-millimeter smooth wall.

21:55

Homogeneous simple fluid, similar to CSF, with no

21:59

septa or calcifications, and the wall may enhance.

22:02

So on the left is a cyst with no enhancing wall.

22:06

On the right is a cyst with a smooth, thin,

22:08

enhancing wall, homogeneous fluid signal intensity.

22:12

Similar to CSF, with no complexity.

22:17

Class two also includes more types,

22:21

but is slightly different from CT

22:23

in that there are fewer of them.

22:24

So the first type, which are

22:26

septated cysts, are the same as CT.

22:29

This is actually the same patient that I showed earlier.

22:32

So these include cystic masses that have

22:35

thin, less than or equal to two millimeters, wall,

22:39

or thin, less than or equal to two millimeters,

22:41

and few septa, and the wall may enhance.

22:47

On MRI, measurements of wall septa,

22:50

irregularities, and nodules should always be

22:53

performed on contrast-enhanced MRI sequences.

22:56

This is a really important, uh,

22:59

feature of Bosniak version 2019.

23:01

The contrast-enhanced images on MRI are the most important.

23:07

The second subtype within class two are homogeneous

23:11

masses that are markedly hyperintense on T2,

23:13

similar to CSF, on non-contrast and enhanced MRIs.

23:18

So these are the same lesions in class one.

23:21

The difference being that there was no contrast media

23:24

available when assessing these T2-weighted images,

23:27

making them a class two as opposed to a class one cyst.

23:33

The third subtype is a markedly T1-weighted hyperintense

23:37

cyst, so this is also similar to the lesion that I

23:41

showed earlier in CT for a nonenhancing soft tissue

23:45

attenuation lesion. On MRI, it turned out to be homogeneously

23:50

markedly T1 hyperintense, greater than 2.5 times

23:54

signal intensity compared to the normal renal parenchyma.

23:58

So this is classified as a class two in Bosniak version 2019.

24:03

You can see on the subtraction image,

24:05

aside from some artifact posteriorly, the

24:08

hemorrhagic cyst was nonenhancing.

24:11

Class II F includes two variants of septated cysts.

24:15

Those that have, um, minimally thickened and smooth wall,

24:22

or minimally thickened and smooth septa, or many septa.

24:27

So on the left are examples of a patient that has a

24:31

minimally thickened smooth septum, and on the right,

24:34

a patient that has numerous thin enhancing septa.

24:40

One of the important differences in class

24:43

II F for MRI compared to, uh, the original

24:47

classification is, again, that assessment should be

24:50

performed primarily on the post-contrast images.

24:54

So here we can see a complex

24:55

cystic mass in the right kidney.

24:58

There's many septations shown on T2.

25:01

However, on the post-contrast image, there is

25:03

no enhancement of any of the septations and only

25:07

smooth, thin enhancement of the wall before.

25:10

This is a class two, not a class II F. That's an

25:14

important difference between version 2019 and the

25:18

original version of the Bosniak classification.

25:21

That assessment on MRI is performed

25:23

primarily on contrast-enhanced images.

25:27

Another subtype within class II F that is new and

25:30

that was added are masses that are heterogeneously

25:33

hyperintense on fat-suppressed T1-weighted images.

25:37

So if you look at the middle image for

25:39

this patient, it looks very similar to the

25:42

markedly T1 hyperintense lesion that I showed earlier.

25:45

The difference, and the key point,

25:47

is the presence of heterogeneity.

25:50

So this one here is a little bit heterogeneous compared

25:53

to the prior, which was completely homogeneous.

25:57

In this case, it was very difficult for the reader to

26:00

confirm the presence of subtraction, uh, of enhancement.

26:03

The subtraction images were slightly corrupted by motion.

26:06

There was some question of some enhancing

26:08

septations within, but not a confident assessment.

26:12

The patient underwent a follow-up exam,

26:16

again showing markedly hyperintense T1

26:19

signal intensity lesion that's grown.

26:22

It's almost doubled in size, and

26:24

it remains slightly heterogeneous.

26:26

And on the post-contrast images, there was again some

26:29

question of internal enhancing septations, but not definite.

26:33

This was resected and confirmed to

26:35

be a papillary renal cell carcinoma.

26:37

So the key point here is that when you have a

26:41

heterogeneous markedly T1 hyperintense or T1

26:46

hyperintense lesion without definite enhancement,

26:49

it would be classified as a class II F.

26:53

So this class is.

26:56

Important because it includes, uh, the subset of papillary

27:00

RCCs that we just can't be sure are enhancing with MRI.

27:04

So they'll fall into class II F now.

27:08

So there, this is a kind of a pitfall, uh, it's

27:10

a corollary case and kind of a pitfall there.

27:13

Here's another lesion.

27:14

Interpolar region, left kidney.

27:16

It's heterogeneously increased signal

27:19

intensity on T1, fat-sat second image.

27:22

However, the difference between this case and the

27:25

former case is that there's definitely thick enhancing

27:28

septation, um, along the medial margin at subtraction MRI.

27:34

It was also present on iodine image from

27:36

a dual-energy CT, and this was confirmed

27:39

to be a papillary renal cell carcinoma.

27:41

So if you have

27:44

heterogeneous increased T1-weighted signal intensity on

27:47

fat-sat pre-contrast, but there's definite enhancement,

27:51

you use the enhancement to classify the

27:54

lesion and not the hyperintense signal on

27:57

T1 and the heterogeneous appearance.

27:59

So this would be a class three, uh, based off

28:03

of the thick wall or septum, not a class II F,

28:06

because of the presence of enhancement.

28:08

So it again emphasizes the point that the highest feature

28:12

is used to assign the Bosniak class, irrespective of

28:16

the number of lower features present within the mass.

28:20

Here's one other consideration within this subtype, which

28:24

is that there are some hemorrhagic cysts which show,

28:29

uh, what I like to call an MRI milk-of-calcium sign.

28:33

That is layering blood products within

28:35

the dependent portion of the cyst.

28:37

So in this case, you have a cystic mass in the

28:40

anterior interpolar region of the left kidney.

28:43

It's almost completely homogeneous.

28:47

T2 bright, similar to CSF, except for

28:49

a homogeneous markedly T1-weighted

28:53

hyperintense focus layering posteriorly.

28:56

That's 2.5 times greater than the renal cortical parenchyma.

29:00

Not enhancing on subtraction image.

29:02

So this is a hemorrhagic cyst, but technically could

29:06

be included in class II F if strictly applying

29:09

the version 2019 classification.

29:13

Class three on MRI is the same as CT.

29:16

It includes one or more thick or

29:18

enhancing irregular walls or septa.

29:21

So here are examples.

29:23

Um, on the left-hand side, there's a patient

29:25

that has a five-millimeter thick septation.

29:29

The middle image is a patient

29:31

with a six-millimeter thick wall.

29:33

And then the third image is a patient that has

29:35

an irregularity along one of the septations.

29:38

So remember, the definition for irregularity is an obtusely

29:42

angled protrusion measuring three millimeters or less.

29:47

So here's a magnified view.

29:49

So you see a protrusion arising from the septum.

29:52

It's obtusely angled, and it measures

29:55

less than or equal to three millimeters.

29:57

So this is an irregularity by definition,

30:00

class three and not a nodule, class four.

30:04

So the final category, um, within MRI

30:07

is class four and very similar to CT.

30:10

It's defined by the presence of nodules, which again are

30:15

protrusions that measure four millimeters or larger when

30:18

they have obtuse angles to the underlying wall or septum.

30:22

Any size when they show acute angles

30:24

to the underlying wall or septum.

30:28

So what is the evidence available in Bosniak version 2019?

30:33

So there's only actually a handful of studies that

30:36

have been published so far, and, um, emerging evidence

30:40

shows that the interobserver agreement is improved or

30:44

similar compared to the original Bosniak classification.

30:48

Um, but there's definitely more room for further data here.

30:52

Particularly since, um, all of the studies published

30:55

to date are single-center retrospective, um, a

31:00

multicenter study would, would, I would be ideal.

31:02

And in particular, there's a need to address inter-

31:05

observer agreement with CT in terms of diagnostic accuracy.

31:11

Overall, there's similar or marginally

31:13

improved accuracy with version 2019.

31:17

The goal of emphasizing specificity with no change

31:21

or similar sensitivity has been, at least in

31:25

preliminary data, realized, and this is due to a

31:29

shift of some class three masses to class II F.

31:33

So this will result in a lower number of benign class

31:38

three masses that unnecessarily undergo surgery.

31:43

The number that was quoted earlier from meta-analysis

31:46

data of 50/50 chance of malignancy in version 2019, that's

31:51

going to get pushed higher, a higher likelihood of malignancy.

31:55

However, the result of that will be that a number of

31:58

class three masses will get shifted into class II F.

32:02

So it's expected, and to some extent being shown, that class

32:07

II F will now have a higher proportion of malignancy

32:10

than in the original classification.

32:14

In terms of formal incorporation of MRI, has that helped?

32:18

If you recall, the important distinction with formal

32:21

incorporation of MRI was emphasis on contrast-enhanced

32:25

MRI images as opposed to relying on T2-weighted images.

32:29

And one study has shown no systematic bias

32:33

using version 2019 towards class assignment,

32:37

comparing CT to MRI.

32:39

Also noted that there are important differences which

32:42

remain between the two systems, between the two modalities.

32:46

So in summary, the Bosniak version 2019 is an

32:49

important proposed revision to the classification

32:52

of cystic renal masses evaluated on CT, MRI,

32:55

and to some extent, ultrasound. Studies are ongoing,

32:59

but preliminarily show similar or marginally

33:02

improved interobserver agreement, similar

33:04

overall accuracy, but with improved specificity.

33:08

A lower number of benign lesions in class

33:11

three, and no systematic bias, at least in one

33:15

study, to class upgrade with MRI compared to CT.

33:19

The Bosniak version 2019 includes important

33:22

changes, updates, and definitions, which aim to

33:25

classify all renal masses and needs careful review.

33:29

So I, I think that needs to be emphasized.

33:31

There's a lot included in version 2019.

33:34

It can be a little bit overwhelming when you first

33:37

read it and try to apply it.

33:39

However, with some experience and some practice, it

33:43

becomes easier as you use it, um, in clinical practice.

33:49

So I'll stop there, and I think

33:51

we have time for a few questions.

33:57

So, uh, first question is, um,

34:00

what is your experience with dual-energy CT

34:03

and looking for septal or wall enhancements?

34:05

So this is actually a great question.

34:07

It's something that we are, um, thinking of studying.

34:11

We do perform dual-energy CT for renal mass assessment

34:15

at our institution, at least in the majority of cases.

34:18

Um, we find that the dual-energy CT is really

34:23

valuable for hyperattenuating lesions and lesions

34:26

which are small and endophytic.

34:29

Um.

34:30

Our preliminary experience is that the dual-energy

34:34

CT probably does not offer any major improvement to

34:38

conventional CT for assessing septal or wall enhancement.

34:42

Um, and the reason, at least in version

34:46

2019, is that the definition

34:49

of enhancement in version 2019 has changed.

34:53

Somewhat ambiguous terms in the original,

34:55

uh, classification, such as perceived or

34:59

measurable enhancement, have been removed.

35:02

So, um, if you're using the original

35:04

classification, I could see how dual-energy CT

35:07

could influence or alter your Bosniak class.

35:12

Because a lesion may show measurable enhancement

35:16

on dual-energy CT that you just might not be

35:18

able to appreciate or measure on conventional CT.

35:21

But the definition has been changed in version 2019.

35:26

The second question I have here is on

35:28

subtraction MRI images of renal cysts.

35:31

Often there is a vague internal signal within the cyst.

35:35

How do you know there is or is not real enhancement?

35:38

So this is a great question.

35:40

Um, and, uh, you know, if you've performed any

35:43

renal MRI in clinical practice, you know that,

35:46

um, the subtraction images are notoriously

35:48

bad, uh, particularly when you need them the most.

35:52

Um, so subtraction imaging really should only be used

35:55

when the lesion is intrinsically bright on T1.

35:59

So if you have a cystic mass

36:01

that does not have any inherently increased T1 signal.

36:05

On the baseline images, you should just

36:08

be comparing the pre-contrast and the post-

36:10

contrast images without the use of subtraction.

36:13

There's no added value of subtraction in that case.

36:16

In lesions that have intrinsically high T1

36:20

signal, where subtraction becomes really important.

36:23

Um, there are a few ways that

36:24

you can improve the subtraction.

36:26

So the first is you should perform renal MRI

36:29

with end-expiration rather than inspiration

36:32

to achieve a better, uh, breath-hold.

36:35

Um, noting that when you do that, the patient's

36:38

going to be less able to hold their breath.

36:41

Um, one other possibility is you can

36:43

apply rapid acceleration techniques.

36:45

So, um, if you have advanced parallel imaging, you can

36:49

push the acceleration factor to really shorten the, um,

36:53

breath-hold to seven, six, sometimes even five seconds.

36:58

Um, and then the last thing that we've tried and

37:01

actually published some, um, good data on is the use of,

37:05

uh, free-breathing or motion compensation techniques.

37:08

So when we perform renal MRI at our institution, we

37:11

always include a backup pre- and post-contrast,

37:15

um, either STAR-VIBE or navigator LAVA.

37:19

So a free-breathing, uh, post-

37:21

contrast image to improve subtraction.

37:25

Um,

37:29

There's a question here about the recommended

37:31

follow-up duration in Bosniak version 2019 for class

37:35

II F. So the, uh, follow-up that's suggested by the

37:38

Bosniak, uh, classification is included in the table.

37:43

And, uh, for class II F, the

37:45

follow-up duration is five years.

37:47

Um, however, it should be noted that

37:50

the surveillance of cystic masses varies by urological

37:55

consensus and guideline, and in many, I, I believe,

37:59

most surveillance protocols for cystic masses

38:02

in the urological literature, there is no,

38:05

um, endpoint to follow-up of a class II F.

38:14

Here is a question, uh, regarding HU cutoffs.

38:17

So this is really important, um, because

38:20

this is something that comes up all the time.

38:22

So, uh, in terms of HU cutoffs, if something is

38:25

20 Hounsfield units or greater, it's enhancing,

38:29

uh, sorry, greater than 20 Hounsfield units.

38:31

So 21 Hounsfield units or more is enhancing,

38:34

with the exception of a lesion that's completely endophytic.

38:38

So in that case, if you suspect that it may

38:41

be due to pseudoenhancement, you could go

38:44

to ultrasound or MRI to confirm that finding.

38:48

If you have a lesion that has enhancement between

38:51

15 to 20, or depending on the literature, 10 to

38:55

20, that could be considered indeterminate range.

38:59

So depending on other imaging

39:01

features such as heterogeneity,

39:03

you could push that lesion towards follow-up or

39:06

MRI, and then less than 10 Hounsfield units is

39:10

not enhancing, and those numbers importantly are

39:13

comparing pre-contrast and nephrographic phase images.

39:17

So that's 100 to 120-second delay, not corticomedullary

39:22

or portal venous phase.

39:26

I think we have time for one more question.

39:31

Um, so there's a question that says, do you think

39:33

we should incorporate microbubble ultrasound?

39:36

Um, so one of the criticisms of the Bosniak version

39:40

2019 classification is that it did, it did to

39:43

some extent incorporate ultrasound, but did not go

39:47

far enough, at least, um, in the opinion of some, um,

39:53

in the incorporation of contrast-enhanced ultrasound.

39:57

So there are ongoing studies, and one of, there's a

39:59

large ongoing study that's organized through the Society

40:02

of Abdominal Radiology Disease Focus Panel on renal

40:06

cell carcinoma, which is evaluating the potential to

40:10

include cystic masses evaluated with contrast-enhanced

40:14

ultrasound into the Bosniak classification.

40:18

Unfortunately, the data regarding

40:21

contrast-enhanced ultrasound is, um,

40:24

compared to CT and MRI, is pretty small and pretty

40:29

much restricted to single-center case-control series,

40:32

so it's not really great data, although it

40:35

certainly looks promising. A larger, um, multicenter

40:39

study validating its use in solid and, in this

40:42

case, cystic renal masses would be really helpful.

40:46

So why don't we stop there?

40:47

If you have any other questions,

40:49

please, um, feel free to email me

40:53

at nida@to.ca or message me through Twitter.

40:57

I'll be happy to answer any questions.

41:01

Thank you.

41:03

All right, everybody.

41:03

As we bring this to a close, I want to thank Dr. Schieda

41:06

for this lecture, and thanks to all of you

41:07

for participating in our noon conference.

41:09

Reminder, this conference will be

41:11

available on demand at mrionline.com.

41:13

In addition to all the previous noon conferences,

41:15

be sure to join us Monday for a lecture from

41:17

Dr. William O'Brien on imaging of the paranasal sinuses.

41:21

You can register for that at mrionline.com and follow

41:23

us on social media at MRI Online for updates

41:26

and reminders of upcoming noon conferences.

41:28

Thanks again, everyone, and have a great day.